Checksum

A checksum or hash sum is a small-size datum from a block of digital data for the purpose of detecting errors which may have been introduced during its transmission or storage. It is usually applied to an installation file after it is received from the download server. By themselves checksums are often used to verify data integrity, but should not be relied upon to also verify data authenticity.

This manual page documents the GNU version of cksum.
cksum computes a cyclic redundancy check (CRC) for each
named file, or the standard input if none are given or
when a file named `-‚ is given. It prints the CRC for
each file along with the number of bytes in the file, and
the file name unless no arguments were given.

cksum is typically used to make sure that files have been
transferred by unreliable means (such as netnews) have not
been corrupted, by comparing the cksum output for the
received files with the cksum output for the original
files. The CRC algorithm is specified by the POSIX.2
standard. It is not compatible with the BSD or System V
sum programs; it is more robust.

–help Print a usage message and exit with a status code
indicating success.